Jim Carrey: Jenny's Son Taught Me How to Love

As he led 8,500 people through the streets of Washington, D.C., Wednesday, hand-in-hand with his daughter, Jane, McCarthy and Evan, the actor told PEOPLE, “He taught me how to love. And without Evan I might never have seen the greatness of Jenny’s spirit.”

Carrey added to the families, lawmakers and other activists gathered to raise awareness about toxins in vaccines that McCarthy is “the source of all that is good” in his life.

That, he explained to PEOPLE, is how he ended up on the frontline of a political movement. “Jenny’s friends would kind of hint around and say, ‘Hey, it would be kind of cool if you got involved in this,’ and I thought to myself, ‘This is just so inevitable. This just can’t not happen.’ If you care about the planet and about children, you have to.”